US2986708A - Expander circuit - Google Patents

Description

May 30, .1961 F. A. BUCKLEY EXPANDER CIRCUIT Filed Aug. 29. 1956 Y E k n 2 3 m n B In Am E P F E .LLW Ell m 2 A 2 F J\&

Y B 1% a i s T Ext O T. U D. -sm 4 3 2 O ATTORNEY United States Patent EXPANDER CIRCUIT Farrell A. Buckley, Manhattan Beach, Calif., assignor to Hughes Aircraft Company, Culver City, Calif., a corporation of Delaware Filed Aug. 29, 1956, Ser. No. 606,910

Claims. Cl. 330-194 The present invention relates to an expander circuit of the type having as one of its characteristics an outputto-input voltage ratio that increases as the input voltage increases.

It is very frequently necessary in the electronic arts to use circuits that can produce an output voltage whose amplitude increases at a more rapid rate than the amplitude of the input voltage or, stated diiferently, whose output-to-input voltage ratio increases as the input voltage increases.

In the past, such a circuit characteristic was obtained by using a single non-linear element, such as copper oxide. However, expansion devices employing such non-linear elements have been subject to at least two shortcomings, namely, it was difiicult to obtain a suitable non-linear element to produce a desired function of the applied voltage and the available non-linear elements generally had undesirable temperature coefiicients, thereby causing undesirable deviations from the circuit characteristic.

It is, therefore, an object of the present invention to provide an expansion circuit that has as one of its characteristics an output-to-input voltage ratio that increases as the amplitude of the input voltage increases.

It is another object of the present invention to provide an expansion circuit whose circuit parameters may be varied to produce a range of desired functions of the applied voltage.

It is a further object of the present invention to provide an expansion circuit whose operation remains stable although the temperatures of its component parts may vary.

The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, toegther with further objects and advantages thereof, will be better understood from the following description considered in connection with the accompanying drawings in which several embodiments of the invention are illustrated by way of examples. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only, and are not intended as a definition of the limits of the invention.

Fig. 1 is a schematic circuit diagram of one embodiment of an expansion circuit according to the present invention;

Fig. 2 is a plot of output-to-input voltages for the expansion circuit of Fig. 1 and illustrates the rise in the output-to-input voltage ratio as the input voltage increases; and

Fig. 3 is a schematic circuit diagram of another embodiment of an expansion circuit according to the present invention.

Referring now to the drawings, there is shown in Fig. 1 a principal embodiment of the expander circuit of the present invention. As shown therein, the expander circuit is designed to accommodate positive signals such that when a positive signal is applied to the circuit, the output- 2,986,708 Patented May 30, 1961 to-input voltage ratio increases as the amplitude of the input signal increases.

The expander circuit comprises a cathode follower stage which includes a triode 10 having an anode 11, a control grid 12 and a cathode 13, and a plurality of cathode resistors, designated 14, :15, 16, 17, arranged as a voltage divider. More specifically, anode 11 is electrically connected to a source of positive voltage designated 13+, control grid 12 is electrically connected to one of a pair of input terminals 18, the remaining input terminal being grounded and cathode 13 is electrically connected through resistors 14, 15, 16, and 17 to a source of negative voltage designated B.

The junction of resistors 14 and 15, designated 20, is electrically connected to ground through a pair of series connected resistors 21 and 22, the junction of resistors 21 and 22 being designated 23. Junction 23 is electrically connected to one of a pair of output terminals 24, the other being grounded.

Junction 23 is also electrically connected through a first resistor 31 and rectifying element 27, to the junction 25 between resistors 15 and 16 and through a second resistor 35 and rectifying element 32 to the junction 26 between resistors 16 and 17. More specifically, the first rectifying element 27 may be a crystal diode having an anode 28 and a cathode 3i], anode 28 being electrically connected to junction point 25 and cathode 30 being electrically connected to one end of the resistor 31, the remaining extremity of which is electrically connected to junction point 23. Similarly, the second rectifying element 32 may be a crystal diode having an anode 33 and a cathode 34, anode 33 being electrically connected to junction point 26 and cathode 34 being electrically connected to one end of the resistor 35, the remaining extremity of which is electrically connected to junction point 23.

By way of example, the voltage sources and the resistors may have the specific values set forth below, namely,

B+=+200 volts. R17=120,O0O ohms.

B= volts. R 150,000 ohms. R =39O0 ohms. R =47,0OO ohms. R15: Ohms. ohms. 11 :6800 ohms. R =5,000 ohms.

Considering now the operation, in the absence of an applied signal, that is, during the quiescent condition of the expander circuit, the voltage potentials at the various junction points are such that crystal diodes 27 and 32 are back-biased or non-conductive and the output voltage at output terminals 24 is zero. More particularly, during quiescence, the small amount of current flowing from source 13-}- through triode 10 and resistors 14, 15, 16, '17 to source B causes voltage drops across these resistors such that the potential at junction point 20 is zero, the potential at junction point 25 is at a first negative value and the potential at junction point 26 is at a second negative value greater by a predetermined amount than at junction point 25. Since one end of resistor 22 is at ground or zero potential, it will be obvious to those skilled in the art that the potential at junction point 23 is also zero. Thus, anodes 28 and 33 are negative biased with respect to cathodes 30 and 34, respectively, and, as previously mentioned, crystal diodes are non-conductive and the output voltage at output terminals 24 is zero.

Typical voltage potentials that may appear at the various junction points during quiescent operation of the expander circuit are as follows:

Junction point 20, 0 volts Junction point 23, 0 volts Junction point 25, -10 volts Junction point 26, -20 volts When a positive voltage signal is applied to control grid 12, the flow of current through triode and, therefore, through resistors 14, 15, 16 and 17 increases with the result that the potentials at junction points 20, 25 and 26 also increase, that is, become less negative. At the same time, current commences to flow through resistors 21 and 22 with the result that a voltage is developed across resistor 22, that is, a positive voltage potential is developed at junction point 23. As the amplitude of the applied signal increases, the fiow of current increases even further, as is well recognized, and the potentials at junction points 20, 23, 25 and 26 correspondingly increase. However, because of the particular values of resistance chosen for resistors 15, 16, 17, 21 and 22, the potentials at junction points 25 and 26 increase more rapidly than at junction point 23. Ultimately, therefore, crystal diode 27 loses its back-bias and becomes current conducting.

When this happens, any additional increase in the amplitude of the applied signal will result in some of the current entering junction point 25 being diverted through crystal diode '27, resistor 31 and resistor 22 to ground. As a consequence thereof, the voltage developed across resistor 22 receives a boost or, stated differently, the outputto-input voltage ratio has been increased as the input voltage was increased. The outpu-t-to-input voltage ratio is still further increased as the amplitude of the applied signal rises because, as the amplitude rises, the back-bias on crystal diode 32 is eventually also removed and still more current is diverted to resistor 22 through crystal diode 32 and resistor 35.

A curve representing output-to-input voltage ratios is shown in Fig. 2 and, as shown therein, the slope of the curve becomes increasingly larger, which means that the output-to-input voltage ratio increases as the input voltage increases. It will be recognized that by varying the circuit parameters, a family of such curves may be obtained. Moreover, it should be noted that the output-toinput voltage ratio may be further accelerated by connecting additional crystal diodes and resistors into the circuit in the manner shown.

The expander circuit of Fig. 1 is adapted to operate with applied positive signals. An expander circuit adapted to operate with applied negative signals is shown in Fig. 3, and, as shown therein, the expander circuit comprises a triode 10 having an anode 11, a control grid 12, and a cathode 13, the anode being electrically connected through a resistor 36 to positive voltage source 13+, the control grid being electrically connected to input terminals l3, and the cathode being grounded. The rest of the expander circuit of Fig. 3 is identical in every respect with the corresponding portion of the expander circuit of Fig. 1, except that in the circuit of Fig. 3, resistor 14 is connected to anode 11 rather than to cathode 13 as in Fig. 1. Accordingly, no further description of circuit construction is deemed necessary.

In operation, when a negative signal is applied to input terminals 18 and, therefore, to control grid 12, the flow of current through triode It is reduced and the flow of current through resistor 14 is correspondingly increased. As the amplitude of the applied signal becomes more negative, the current flow through triode 19 is further reduced and the flow of current through resistor 14 is further increased. Thus, as before, the back-bias on crystal diodes 27 and 32 are successively removed and the outputto-input voltage ratio is made an increasing function of the input voltage.

Having thus described the invention, what is claimed as new is:

1. An expander circuit for producing an output voltage in response to an input voltage such that the output-toinput voltage ratio increases as the input voltage increases, said circuit comprising: a first voltage divider network including first, second and third resistors electrically connected in series in the order named from a first terminal to a second terminal, said first and second resistors being connected to each other at a first junction point and said second and third resistors being connected to each other at a second junction point; a second voltage divider network including fourth and fifth resistors electrically connected in series in the order named from said first junction point to a third terminal maintained at a substantially fixed reference potential, said fourth and fifth resistors being connected to each other at a third junction point; an output terminal connected to said third junction point; a rectifying element and a sixth resistor electrically connected in series from said second junction point to said third junction point, said rectifying element being poled in a manner to allow current to fiow from said second junction point to said third junction point; means connected to said first and second terminals for maintaining said first terminal positive and said second terminal negative with respect to said substantially fixed reference potential thereby to normally back-bias said rectifying element; and means responsive to said input voltage and electrically coupled to said first terminal for varying the current flow through said first resistor in accordance with the amplitude thereof.

2. An expander circuit for producing an output voltage in response to an input voltage such that the output-toinput voltage ratio increases as the input voltage increases, said circuit comprising: first and second resistors; a first plurality of resistors electrically connected in series between one end of said first resistor and one end of said second resistor; third and fourth resistors electrically connected in series in the order named from said one end of said first resistor to a reference terminal maintained at a substantially fixed potential, said third and fourth resistors being connected to each other at a junction point; means connected to said first and second resistors for maintaining the remaining end of said first resistor positive and the remaining end of said second resistor negative with respect to said substantially fixed potential; means coupled to the other end of said first resistor and responsive to the input voltage for varying the flow of current through said first resistor in accordance with the amplitude thereof; and a rectifying element and resistor connected in series from said junction point to each of the common junctions of said first plurality of resistors and to said one end of said second resistor, said rectifying elements being poled in a manner to be normally backbiased and to be successively rendered forward-biased as the amplitude of the input voltage increases.

3. In an expander circuit for producing an output voltage in response to an input voltage such that the outputto-input voltage ratio increases as the input voltage increases, the combination comprising: first and second resistors; a first plurality of resistors electrically connected in series between one end of said first resistor and one end of said second resistor; third and fourth resistors electrically connected in series in the order named from said one end of said first resistor to a reference terminal maintained at a substantially fixed potential, said third and fourth resistors being connected to each other at a junction point; a second plurality of resistors corresponding in number to said first plurality of resistors, one end of each of said second plurality of resistors being electrically connected to said junction point; means connected to said first and second resistors for maintaining the remaining end of said first resistor positive and the remaining end of said second resistor negative with respect to said substantially fixed potential; and a plurality of rectifying elements corresponding in number to said first plurality of resistors electrically connected from the remaining ends of said second plurality of resistors to respective junctions between said first plurality of resistors and to said one end of said second resistor, said rectifying elements being poled in the same direction in a manner to normally be back-biased.

4. An expander circuit for producing an output voltage at first and'second output terminals in response to an input voltage applied to first and second input terminals such that the output-to-input voltage ratio increases as the input voltage increases, said second output terminal and said second input terminal being maintained at a substantially fixed reference potential, said circuit comprising: an electron discharge device having at least an anode, a control grid and a cathode, the control grid being electrically connected to sair first input terminal; means connected to said anode for maintaining said anode at a potential that is positive relative to said substantially fixed reference potential; first and second resistors, one end of said first resistor being electrically connected to said cathode and one end of said second resistor being electrically connected to a terminal maintained at a potential that is negative relative to said substantially fixed reference potential; a first plurality of resistors electrically connected in series between the other ends of said first and second resistors; third and fourth resistors electrically connected in series in the order named from said other end of said first resistor to said second output terminal, said third and fourth resistors being connected to each other at a junction point, said junction point being electrically connected to said first output terminal; and a second plurality of serially connected resistors and rectifying elements corresponding in number to said first plurality of resistors and being electrically connected from said junction point to successive junctions between said first plurality of resistors and said other end of said second resistor, said rectifying elements normally being back-biased and being successively rendered forward-biased as the amplitude of the input voltage increases.

5. An expander circuit for producing an output voltage at first and second output terminals in response to an input voltage applied across first and second input terminals such that the output-to-input voltage ratio increases as the input voltage increases, said second output terminal and said second input terminal being maintained at a substantially fixed reference potential, said circuit comprising: an electron discharge device having at least an anode, a control grid and a cathode, the control grid being electrically connected to said first input terminal; a plate resistor having one end electrically connected to said anode and a remaining end maintained at a potential that is positive with respect to said reference potential; first and second resistors, one end of said first resistor being electrically connected to said anode and one end of said second resistor being maintained at a potential that is negative with respect to said reference potential; a first plurality of resistors electrically connected in series between the other ends of said first and second resistors, third and fourth resistors electrically connected in series in the order named from the other end of said first resistor to said second output terminal, said third and fourth resistors being connected to each other at a junction point, said junction point being electrically connected to said first output terminal; a second plurality of resistors corresponding in number to said first plurality of resistors, each of said second plurality of resistors being electrically connected in series with a unidirectionally conducting device from said junction point to the junctions between said first plurality of resistors and to the remaining end of said second resistor, said unidirectionally conducting devices normally being back-biased and being successively rendered forward-biased as the amplitude of the input voltage increases.

References Cited in the file of this patent UNITED STATES PATENTS 2,548,913 Schreiner et a1. Apr. 17, 1951 2,553,673 Purington May 22, 1951 2,581,124 Moe Jan. 1, 1952 2,697,201 Harder Dec. 14, 1954 2,769,137 Creusere Oct. 30, 1956 2,906,871 Crawford Sept. 29, 1959

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